In recent years, from the viewpoint of environmental protection, various electric devices have generally been controlled by inverter circuits for promoting energy saving and highly efficient operation. Particularly, in car industries, since hybrid electric vehicles (hereinafter, referred to as HEVs) that run with an electric motor and an engine appeared on the market, car manufacturers have been promoting environment-friendly technology development focused on energy saving and high efficiency.
Since an electric motor for HEVs operates in a high service voltage range, such as several hundred volts, manufacturers focus on a capacitor having preferable electric characteristics, such as high withstand voltage and low loss, as being suitable for the HEV motor. Besides, in response to demands of the market on maintenance-free components, the use of the metallized film capacitor is increasing because of its extremely long life.
A metallized film capacitor used for HEVs is used for smoothing an AC component of DC power supply. In that case, an AC ripple current flowing in a DC power supply increases heat generated in the capacitor, so that heating margins of the capacitor decreases. Therefore, a metallized film capacitor with high heat-dissipation performance has been demanded.
FIGS. 4A to 4C are schematic views of metallized film capacitor 1. Metallized film capacitor 1 includes winding cores 2 and 3 made of aluminum and capacitor element 4 including a metallized film wound around winding cores 2 and 3. Winding cores 2 and 3 are apart from each other at the center of the capacitor to obtain electrical isolation between positive and negative electrodes of winding cores 2 and 3. Outer ends of winding cores 2 and 3 are connected to sprayed-metal electrode 5 (the positive electrode) and sprayed-metal electrode 6 (the negative electrode), respectively. Sprayed-metal electrodes 5 and 6 are connected to a bus bar to be drawn to the outside. Winding cores 2 and 3 are made of aluminum and therefore provide relatively high heat conduction. Generated heat is transferred to the bus bar via sprayed-metal electrodes 5 and 6 and further led to the outside, so that heat generation in capacitor element 4 is suppressed.
Patent literature 1 describes a conventional capacitor similar to metallized film capacitor 1.
In metallized film capacitor 1, heat generated in capacitor element 4 cannot be dissipated sufficiently through winding cores 2 and 3.